General Pharmacology Practice Questions

Q: Which of the following is a cause for reduced bioavailability?

High first-pass metabolism. **Explanation:** **Bioavailability (F)** is defined as the fraction of an administered dose of unchanged drug that reaches the systemic circulation. **Why Option A is Correct:** **High first-pass metabolism** (or pre-systemic metabolism) occurs when a drug is metabolized in the gut wall or the liver before it reaches the systemic circulation. Drugs taken orally travel via the portal vein to the liver; if the liver extensively metabolizes the drug during this first pass, the amount of active drug entering the general circulation is significantly reduced, thereby lowering bioavailability. Examples include Nitroglycerin, Propranolol, and Lidocaine. **Why Other Options are Incorrect:** * **B. Increased absorption:** Enhanced absorption increases the amount of drug entering the bloodstream, which would increase (not reduce) bioavailability. * **C. Intravenous (IV) administration:** By definition, IV administration bypasses the absorption phase and first-pass metabolism. It provides **100% bioavailability (F=1)**, the highest possible value. * **D. High lipid solubility:** Lipid solubility generally facilitates the passage of drugs across biological membranes (like the GI mucosa), typically leading to better absorption and higher bioavailability. **NEET-PG High-Yield Pearls:** * **Formula:** Bioavailability = (AUC oral / AUC IV) × 100. * **Nitroglycerin:** Has such high first-pass metabolism (>90%) that it is administered sublingually to bypass the liver and ensure rapid systemic entry. * **Hepatic Extraction Ratio (ER):** Drugs with a high ER (e.g., Morphine, Verapamil) have low oral bioavailability. * **Bioequivalence:** Two formulations of the same drug are bioequivalent if they show the same rate and extent of bioavailability.

Q: Cyproheptadine acts on which of the following receptors?

D2. **Explanation:** Cyproheptadine is a unique pharmacological agent known for its **multi-receptor antagonist** properties. While it is primarily classified as a first-generation antihistamine, its clinical utility and side-effect profile are dictated by its action on several receptor systems. **1. Why Option A (D2) is the Correct Answer (in the context of this specific question):** Cyproheptadine acts as an antagonist at **H1, 5-HT2A, and Muscarinic** receptors. However, it **does not** have significant activity at **Dopamine (D2) receptors**. In NEET-PG "Except" or "Which of the following" questions, identifying the receptor *not* blocked by the drug is a common testing pattern. Therefore, D2 is the correct choice as it is the outlier. **2. Analysis of Other Options:** * **Option B (H1):** Cyproheptadine is a potent **H1-receptor antagonist**, used to treat allergic rhinitis and urticaria. * **Option C (Muscarinic):** Like most first-generation antihistamines, it possesses significant **anticholinergic (anti-muscarinic)** activity, leading to side effects like dry mouth and urinary retention. * **Option D (5-HT2A):** This is a high-yield fact. Cyproheptadine is a powerful **5-HT2A antagonist**. This property makes it the drug of choice for managing **Serotonin Syndrome**. **Clinical Pearls for NEET-PG:** * **Serotonin Syndrome:** Cyproheptadine is the specific antidote. * **Appetite Stimulant:** Due to its 5-HT2 blockade in the hypothalamus, it is used off-label to stimulate appetite in children and patients with cachexia. * **Other Uses:** It is used in the prophylaxis of **Migraine** and the management of **Post-gastrectomy Dumping Syndrome**. * **Key Contraindication:** Due to its anticholinergic effects, it should be avoided in patients with **Glaucoma** and **BPH**.

Q: Which of the following drugs is not metabolized by acetylation?

Metoclopramide. **Explanation:** The question tests your knowledge of **Phase II metabolic reactions**, specifically **Acetylation**. This process is mediated by the enzyme **N-acetyltransferase (NAT)**. **Why Metoclopramide is the correct answer:** Metoclopramide is primarily metabolized in the liver via **Glucuronidation** and **Sulfation** (Phase II reactions), as well as oxidation. It does not undergo acetylation. It is a dopamine (D2) antagonist used as a prokinetic and antiemetic. **Why the other options are incorrect:** Options A, B, and C are classic examples of drugs metabolized by acetylation. A useful mnemonic to remember these is **"SHIP"**: * **S – Sulfonamides** (and **Dapsone**, which is a sulfone) * **H – Hydralazine** * **I – Isoniazid (INH)** * **P – Procainamide** * **Isoniazid (INH):** The prototype drug for acetylation. It is metabolized by NAT2. * **Dapsone:** Used in leprosy; its metabolite monoacetyl dapsone is a marker of acetylation status. * **Hydralazine:** An antihypertensive that carries a high risk of drug-induced lupus in certain patients. **High-Yield Clinical Pearls for NEET-PG:** 1. **Genetic Polymorphism:** Acetylation shows bimodal distribution in the population, dividing individuals into **Fast Acetylators** and **Slow Acetylators**. 2. **Slow Acetylators:** These individuals are at a higher risk of toxicity from "SHIP" drugs. Specifically, they are prone to **Drug-Induced Lupus Erythematosus (DILE)** (especially with Hydralazine and Procainamide) and **Peripheral Neuropathy** (with Isoniazid). 3. **Fast Acetylators:** They may require higher doses of these drugs to achieve therapeutic levels and are at a higher risk of **Hepatotoxicity** with Isoniazid due to the rapid formation of the metabolite acetylhydrazine.

Q: All the following drugs undergo metabolism by acetylation EXCEPT?

Phenytoin. **Explanation:** The correct answer is **Phenytoin**. Metabolism by **acetylation** is a Phase II reaction catalyzed by the enzyme **N-acetyltransferase (NAT)**. This pathway is genetically determined, leading to the classification of individuals as "fast" or "slow" acetylators. **Why Phenytoin is the correct answer:** Phenytoin does not undergo acetylation. Instead, it is metabolized in the liver primarily via **Phase I oxidation** (hydroxylation) by the cytochrome P450 system (specifically **CYP2C9** and **CYP2C19**). A unique feature of phenytoin metabolism is that it follows **zero-order kinetics** (capacity-limited metabolism) at therapeutic or high concentrations, making its plasma levels highly sensitive to dose adjustments. **Why the other options are incorrect:** Options A, B, and C are classic examples of drugs metabolized by acetylation. They can be remembered using the mnemonic **"SHIP"**: * **S**ulfonamides (e.g., Sulfadiazine) * **H**ydralazine (Option B) * **I**soniazid (Option A) * **P**rocainamide (Option C) **Clinical Pearls for NEET-PG:** 1. **Drug-Induced Lupus Erythematosus (DILE):** Slow acetylators are at a significantly higher risk of developing DILE when taking Hydralazine, Isoniazid, or Procainamide. 2. **Isoniazid Toxicity:** Slow acetylators are more prone to peripheral neuropathy (due to Vitamin B6 deficiency), while fast acetylators may be more prone to hepatotoxicity due to the rapid formation of the metabolite acetylhydrazine. 3. **Genetic Polymorphism:** Acetylation is the classic example of pharmacogenetic variation in drug metabolism. **High-Yield Mnemonic for Acetylation:** **"SHIP"** (Sulfonamides, Hydralazine, Isoniazid, Procainamide).

Q: The skeletal muscle relaxant, vecuronium, acts at cholinergic receptors where it exhibits:

Affinity but no efficacy. ### Explanation **1. Why Option A is Correct:** Vecuronium is a **competitive (non-depolarizing) neuromuscular blocker**. In pharmacology, an **antagonist** is defined as a drug that has **affinity** (the ability to bind to a receptor) but lacks **intrinsic activity/efficacy** (the ability to activate the receptor and produce a biological response). Vecuronium competes with acetylcholine (ACh) for the nicotinic receptors ($N_m$) at the neuromuscular junction. By binding to the receptor without activating it, it prevents ACh from binding, thereby inhibiting muscle contraction and causing paralysis. **2. Why Other Options are Incorrect:** * **Option B (Efficacy but no affinity):** This is pharmacologically impossible. A drug must first have affinity (bind) to a receptor before it can exert any efficacy. * **Option C (Receptor upregulation):** While chronic blockade of receptors can lead to upregulation (an increase in receptor number), this is a long-term compensatory mechanism and not the primary mechanism of action of vecuronium. * **Option D (Affinity and efficacy):** This describes an **agonist**. Succinylcholine (a depolarizing blocker) initially shows affinity and efficacy (causing fasciculations) before causing a block. Vecuronium, being non-depolarizing, has no efficacy. **3. NEET-PG Clinical Pearls:** * **Reversibility:** The action of vecuronium can be reversed by Acetylcholinesterase inhibitors like **Neostigmine**, which increase ACh levels to outcompete the blocker. * **Sugammadex:** A specific reversal agent that encapsulates vecuronium molecules, rendering them inactive. * **Metabolism:** Vecuronium is primarily excreted via **bile** (partially metabolized by the liver), making it safer than pancuronium in patients with renal failure. * **Cardiovascular Stability:** Unlike d-tubocurarine, vecuronium does not cause significant histamine release or ganglion blockade, ensuring hemodynamic stability.

Q: Succinylcholine is contraindicated in all the following conditions except:

Rapid sequence intubation. **Explanation:** Succinylcholine is a **depolarizing neuromuscular blocker** that acts as an agonist at the nicotinic acetylcholine receptors (nAChR). Its primary clinical utility is in **Rapid Sequence Intubation (RSI)** because of its rapid onset (30–60 seconds) and short duration of action (5–10 minutes), allowing for quick airway control. **Why Option C is Correct:** Rapid sequence intubation is the **primary indication** for Succinylcholine, not a contraindication. It is preferred in emergency settings where the patient has a "full stomach" to prevent aspiration. **Why Other Options are Contraindicated:** The common mechanism for contraindication in options A, B, and D is the risk of **life-threatening hyperkalemia**. * **Burns (Option A):** After 24–48 hours of a major burn, there is an "upregulation" of extrajunctional acetylcholine receptors. Succinylcholine causes prolonged depolarization of these receptors, leading to a massive efflux of potassium. * **Muscular Dystrophy (Option B):** In conditions like Duchenne muscular dystrophy, Succinylcholine can cause rhabdomyolysis, hyperkalemia, and cardiac arrest. * **Neuromuscular Disease (Option D):** Conditions like stroke, spinal cord injury, or prolonged immobilization also lead to receptor upregulation, making the patient highly susceptible to hyperkalemic cardiac arrest. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Agonist at nAChR causing persistent depolarization (Phase I block). * **Metabolism:** Rapidly hydrolyzed by **Pseudocholinesterase** (Butyrylcholinesterase). * **Side Effects:** Muscle fasciculations (can be prevented by a small dose of non-depolarizing blocker), malignant hyperthermia (treated with **Dantrolene**), and increased intraocular/intragastric pressure. * **Genetic Variation:** Patients with atypical pseudocholinesterase experience prolonged apnea after Succinylcholine administration.

Q: Quinine-induced thrombocytopenia is a type of?

Antibody-mediated reaction. **Explanation:** **Correct Answer: A. Antibody-mediated reaction** Quinine-induced thrombocytopenia (QITP) is a classic example of **drug-induced immune thrombocytopenia (DITP)**. The underlying mechanism is a **Type II Hypersensitivity reaction**. Quinine acts as a hapten or alters platelet surface glycoproteins (specifically GPIb/IX or GPIIb/IIIa), making them antigenic. This triggers the production of drug-dependent antibodies (usually IgG) that bind to platelets only in the presence of the drug. These antibody-coated platelets are then rapidly cleared by the splenic macrophages, leading to a profound drop in platelet count. **Why other options are incorrect:** * **B. Dose-related toxicity:** QITP is not related to the plasma concentration of the drug. Even minute amounts (e.g., quinine in tonic water) can trigger a severe reaction in sensitized individuals. * **C. Idiosyncratic reaction:** While the reaction occurs in a small subset of patients, "Idiosyncratic" is a broad term for unpredictable reactions. "Antibody-mediated" is the specific, more accurate immunologic mechanism required for NEET-PG. * **D. Inhibition of platelet production:** This refers to bone marrow suppression (e.g., by chemotherapy or thiazides). Quinine causes peripheral destruction of mature platelets, not a failure of megakaryocytes in the marrow. **NEET-PG High-Yield Pearls:** * **Common Culprits of DITP:** Quinine, Quinidine, Sulfonamides, Heparin (HIT), and Vancomycin. * **Clinical Presentation:** Sudden onset of petechiae, mucosal bleeding, or "wet purpura" within hours of drug ingestion. * **Diagnosis:** Platelet count often drops severely (<20,000/µL). * **Management:** Immediate discontinuation of the drug is the most critical step. Recovery usually occurs within 7–10 days as the drug is cleared from the system.

Q: All the following drugs cross the blood-brain barrier EXCEPT one?

Dopamine. ### Explanation The ability of a drug to cross the **Blood-Brain Barrier (BBB)** depends on its lipid solubility, molecular size, and ionization state. The BBB is a highly selective semipermeable border of endothelial cells with tight junctions that prevents the passage of large or highly polar (hydrophilic) molecules. **Why Dopamine is the Correct Answer:** **Dopamine** is a highly polar, ionized catecholamine. Due to its hydrophilic nature, it cannot cross the BBB. In clinical practice, this is why dopamine cannot be used to treat Parkinson’s disease. Instead, its precursor **Levodopa (L-Dopa)** is used because it can cross the BBB via a neutral amino acid transporter, where it is then decarboxylated into dopamine within the CNS. **Analysis of Incorrect Options:** * **Morphine:** While less lipid-soluble than heroin, morphine is still lipophilic enough to cross the BBB and exert its analgesic effects on opioid receptors in the brain. * **Propranolol:** This is a highly lipid-soluble, non-selective beta-blocker. Its high CNS penetration explains its effectiveness in treating essential tremors and its potential side effects like vivid dreams or depression. * **Ether:** As a volatile general anesthetic, ether is highly lipid-soluble. All general anesthetics must cross the BBB rapidly to induce anesthesia. **NEET-PG High-Yield Pearls:** 1. **Physiological "Gaps":** The BBB is absent in the **Circumventricular Organs** (e.g., Area Postrema/CTZ, Posterior Pituitary). This allows the CTZ to detect toxins in the blood and induce vomiting. 2. **Inflammation:** Meningitis increases the permeability of the BBB, allowing drugs like **Penicillin G** (which normally has poor CNS penetration) to reach therapeutic levels in the CSF. 3. **Antihistamines:** 1st-generation antihistamines (e.g., Diphenhydramine) cross the BBB causing sedation, whereas 2nd-generation (e.g., Loratadine) do not.

Q: What is a Type E adverse drug reaction?

Withdrawal reaction. **Explanation:** Adverse Drug Reactions (ADRs) are most commonly classified using the **Rawlins and Thompson classification**, which categorizes reactions from Type A to Type F based on their mechanism and timing. **Why Option D is Correct:** **Type E (End-of-use)** reactions occur when a drug is suddenly discontinued. These are **withdrawal reactions** [1]. The body, having adapted to the presence of the drug (physiological dependence), reacts to its absence [1]. Classic examples include: * **Beta-blockers:** Rebound hypertension or tachycardia. * **Opioids/Benzodiazepines:** Withdrawal syndrome (insomnia, anxiety, tremors). * **Clonidine:** Rebound hypertensive crisis. **Why the Other Options are Incorrect:** * **Option A (Toxicity):** This is a **Type A (Augmented)** reaction. It is dose-dependent and a predictable extension of the drug’s primary pharmacology (e.g., bleeding with Heparin) [2], [4]. * **Option B (Augmented pharmacologic effect):** This is the definition of **Type A** reactions [4]. They are common, predictable, and usually managed by dose adjustment [4]. * **Option C (Teratogenesis):** This falls under **Type D (Delayed)** reactions. These occur long after the drug exposure, including carcinogenesis and teratogenicity (e.g., Phocomelia with Thalidomide) [3]. **NEET-PG High-Yield Pearls:** * **Type A (Augmented):** Dose-related, predictable (e.g., Hypoglycemia with Insulin) [2]. * **Type B (Bizarre):** Non-dose related, unpredictable, idiosyncratic (e.g., Anaphylaxis with Penicillin). * **Type C (Chronic):** Occurs with long-term use (e.g., Analgesic nephropathy). * **Type D (Delayed):** Carcinogenicity/Teratogenicity [3]. * **Type E (End-of-use):** Withdrawal [1]. * **Type F (Failure):** Unexpected failure of therapy (e.g., Drug interactions reducing oral contraceptive efficacy).

Q: H1 antagonist has all the functions except?

Decreased gastric acid secretion. **Explanation:** The question tests the distinction between Histamine receptor subtypes and their physiological roles. Histamine acts via four primary receptors ($H_1$ to $H_4$), each coupled to different signaling pathways and located in distinct tissues. **Why Option C is Correct:** Gastric acid secretion is mediated exclusively by **$H_2$ receptors** located on the parietal cells of the stomach. Activation of $H_2$ receptors increases cAMP, leading to acid production. Therefore, $H_1$ antagonists have no effect on gastric acid; this function requires $H_2$ blockers like Ranitidine or Famotidine. **Analysis of Incorrect Options:** * **A. Anti-pruritic:** $H_1$ receptors are located on peripheral nerve endings. Blocking them inhibits the "itch" sensation, making $H_1$ blockers the mainstay for treating urticaria and allergic dermatitis. * **B. Sedation:** First-generation $H_1$ antihistamines (e.g., Diphenhydramine, Promethazine) are highly lipophilic and cross the blood-brain barrier. They block central $H_1$ receptors involved in wakefulness, leading to sedation. * **C. Antiemetic:** Certain $H_1$ blockers (especially Promethazine and Doxylamine) have significant anticholinergic activity and act on the vestibular apparatus and the chemoreceptor trigger zone (CTZ), making them effective for motion sickness and morning sickness. **NEET-PG High-Yield Pearls:** * **Second-generation $H_1$ blockers** (e.g., Cetirizine, Loratadine, Fexofenadine) are non-sedating because they have poor CNS penetration. * **Terfenadine and Astemizole** (older 2nd gen) were withdrawn due to **QT interval prolongation** (Torsades de pointes) when co-administered with CYP3A4 inhibitors (e.g., Erythromycin, Ketoconazole). * **Fexofenadine** is the active metabolite of Terfenadine and is safe (no cardiotoxicity).

Question 1

Which of the following is a cause for reduced bioavailability?

Accepted Answer

High first-pass metabolism

Answer

Increased absorption

Answer

Intravenous drug administration

Answer

High lipid solubility

Question 2

Cyproheptadine acts on which of the following receptors?

Accepted Answer

D2

Answer

H1

Answer

Muscarinic

Answer

5HT2A

Question 3

Which of the following drugs is not metabolized by acetylation?

Accepted Answer

Metoclopramide

Answer

Isoniazid

Answer

Dapsone

Answer

Hydralazine

Question 4

All the following drugs undergo metabolism by acetylation EXCEPT?

Accepted Answer

Phenytoin

Answer

Isoniazid

Answer

Hydralazine

Answer

Procainamide

Question 5

The skeletal muscle relaxant, vecuronium, acts at cholinergic receptors where it exhibits:

Accepted Answer

Affinity but no efficacy

Answer

Efficacy but no affinity

Answer

Receptor upregulation

Answer

Affinity and efficacy

Question 6

Succinylcholine is contraindicated in all the following conditions except:

Accepted Answer

Rapid sequence intubation

Answer

Burns

Answer

Muscular dystrophy

Answer

Neuromuscular disease

Question 7

Quinine-induced thrombocytopenia is a type of?

Accepted Answer

Antibody-mediated reaction

Answer

Dose-related toxicity

Answer

Idiosyncratic reaction

Answer

Inhibition of platelet production

Question 8

All the following drugs cross the blood-brain barrier EXCEPT one?

Accepted Answer

Dopamine

Answer

Morphine

Answer

Propranolol

Answer

Ether

Question 9

What is a Type E adverse drug reaction?

Accepted Answer

Withdrawal reaction

Answer

Toxicity

Answer

Augmented pharmacologic effect

Answer

Teratogenesis

Question 10

H1 antagonist has all the functions except?

Accepted Answer

Decreased gastric acid secretion

Answer

Anti-pruritic

Answer

Sedation

Answer

Antiemetic

General Pharmacology — MCQs

General Pharmacology — MCQs

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